Highly Undetectable steGO (HUGO steganography) is a well-known image steganography method proposed in recent years. The security of HUGO steganography is analyzed in this paper, and a corresponding steganalysis method is proposed based on the blind coding parameters recognition. Firstly, the principle of covert communication based on HUGO steganography and the characteristics of the Syndrome-Trellis codes (STCs) used in HUGO are analyzed; and then the potential security risk of HUGO is pointed out; Secondly, based on the idea of the blind parameters recognition for channel coding, the submatrix parameter of Multimed Tools Appl STCs is recognized correctly, and thus the message embedded by HUGO can be extracted correctly by decode algorithm of STCs. A series of experimental results show that the proposed steganalysis method can not only detect the stego-images reliably, but also extract the embedded message correctly; these validated the existence of security flaw of HUGO steganography.

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In digital steganography, due to difficulties estimating the JPEG cover image, it is still very hard to accurately locate the hidden message embedded in a JPEG image. Therefore, this study proposes a payload location method for a category of pseudo-random scrambled JPEG image steganography. In order to estimate the quantized discrete cosine transform coefficients in the cover JPEG image, a cover JPEG image estimation method is proposed based on co-frequency sub-image filtering. The proposed payload location method defines a general residual, uses the estimated cover JPEG image to compute the residuals, and then employs the mean residuals of multiple stego images embedded along the same path to distinguish the stego positions. The proposed cover JPEG image estimation method constructs 64 co-frequency sub-images, and then filters the sub-image to estimate the cover JPEG image. Finally, using these methods, payload location algorithms are designed for two common JPEG image steganography algorithms: JSteg and F5. Experimental results show that the proposed location algorithms can effectively locate the stego positions in both JSteg and F5 steganography when the investigator possesses multiple stego images embedded along the same path. In addition, the location results can also be used to recover the steganography key to extract the embedded secret messages.